Solid/liquid separation operations must be performed in different process steps in the production of wine and fruit juice. This separation may be accomplished by conventional separating processes such as sedimentation, centrifuging, cake filtration, etc., or by so-called “cross-low filtration” as described in the publication by Karbachsch, M., Pototschnigg, S., and Bauer, R. “Einsatz der Cross-Flow-Filtration in der Getränkeindustrie, Kellerwirtschaft” [Use of Cross-Flow filtration in the Beverage Industry, Cellar Management]. This filtration differs from so-called “dead-end filtration” in that a shearing strain gradient acting transversely to the direction of filtration flows tangentially over the surface of the diaphragm. Formation of a cover layer on the surface of the diaphragm is suppressed or reduced to the minimum as a result. Disadvantages of cross-flow filtration are that the type of particles to be separated cannot be affected and that the liquid to be filtered must be circulated by pump until passage through the diaphragm occurs. The associated mechanical and/or thermal stress applied to the liquid to be filtered often results in loss of quality.
The so-called kieselguhr filtration technique is often employed for prefiltering conventionally. However, filtration free of yeast can be achieved only at great cost, even when medium-fine or fine kieselguhr is used. In addition, the kiesetguhr used must be replaced after a period of operation depending, among other things, on the particle charge of the liquid to be filtered. The used kieselguhr must be disposed.
To permit continuation of filtration during cleaning of a filter or other maintenance operations, so-called standby filter lines are often provided and are engaged only if a filter line in operation must be shut down. The result is that a significant part of the filtration equipment, the elements of the standby line, remain largely unused even though they must be kept ready for use.
DE-A-196 07 740 A1 discloses a filtration system with a preliminary filtering stage including three preliminary filter housings and an end filtering stage including two end filter housings. The end filtering stage is mounted downstream from the prefiltering stage as a specific modular unit. Each of the housings has a pressure differential measurement device by means of which the pressure differential between housing inlet and housing outlet is determined in each instance. The accompanying “flux” is determined by the volume flow equipment serving simultaneously as volume metering equipment and being mounted in the filtrate collecting line. In customary filtration, only a preliminary filter housing together with an end filter housing mounted in line performs the filtration. Every possible combination is conceivable, that is, while the preliminary filter lines and the end filter lines are controlled on the same principle, they are controlled separately and with different limiting values. A system designed for this purpose is usually employed for lime disinfection of beer or the like. Operation of the system in which several preliminary filter stages and end filter stages are used simultaneously side by side is not possible with the conventional systems. This aspect restricts their efficiency correspondingly. Even if regeneration of a preliminary filter or end filter is carried out, only a preliminary filter or an end filter remains in the filter line at all times. This limitation is a factor contributing to the very low efficiency of the conventional system.
In addition, the conventional filtration system is operated with a constant flow volume, something which may result in blocking of the respective preliminary filter or end filter, if one of the filters is removed from the filtration process, either deliberately or unintentionally, or becomes unusable, as a result of fouling, for example.
DE-A-37 00 804 discloses a process and a system for concentration of substances present in dispersed or colloidal solutions from a greatly diluted initial product by ultrafiltration, in particular for preparation of active ingredients in the medical or pharmaceutical fields. After preliminary selection of the parameters represented by supply pressure and pressure differential, a control unit is used to keep the pressure differential constant during an ultrafiltration program by acting on the supply flow of the pump and by acting on the counterpressure by a choke. An optimal filtration result is obtained throughout the program, despite the varying viscosity of the material to be filtered. Hence, the conventional solution discloses reduction in the volume flows as a function of the pressure differential in ultrafiltration systems. In each instance, a battery of filter elements is connected in series parallel to each other in a circuit taking unfiltered material from a common reservoir. In synchronous operation, they pass the filtrate on continuously to a common collecting point during operation. No provision is made in this process for regeneration of individual filter elements.